Geant4: an update

1
Geant4 an update
An overview of Geant4s recent developments

• John Apostolakis, CERN
• Makoto Asai, SLAC
• for the Geant4 collaboration

2
Outline

• Brief introduction to Geant4
• Physics highlights
• Modeling
• validation
• New capabilities
• Detector description and collision detection
• Some current Developments
• In progress
• Planned for 2003

3
Introduction
Part 1

• Context
• Toolkit structure

4
GEANT 4 introduction

• Detector simulation tool-kit for HEP
• offering alternatives, allowing for tailoring
• Software Engineering and OO technology
• provide the method for building, maintaining it.
• Requirements from HEP other domains
• LHC, heavy ions, CP violation, cosmic rays
• medical and space science applications
• World-wide collaboration
• RD44 1994-1998
• MoU 1999-today

5
Geant4 Overview

• Extensive transparent physics models
• electromagnetic, hadronic, optical, decay,
• Powerful structure and kernel
• tracking, stacks, geometry, hits,
• Interfaces
• visualization, GUI, persistency.
• Efficiency enhancing techniques
• Framework for fast simulation (shower
  parameterization)
• Variance reduction / event biasing

6
Physics Highlights
Part 2

• Modeling
• and
• Validation

7
Physics Development Highlights

• Geant4 releases Dec 2001-today included
• New EM processes
• And improvements to existing processes
• New theoretical hadronic models
• In particular for the cascade energy range
• The release of tailored physics lists
• For different hadronics use cases.
• Numerous physics improvements
• Including, for example
• Charge state for recoils
• Improved X-sections for e-Nuclear, with hard
  scattering

8
Significant developments in EM (std) in 2002

• Multiple scattering (L. Urban)
• Angular distributions (see next slides)
• Ultra relativistic energies (H. Burkardt, S.
  Kelner, R. Kokoulin)
• g m m process
• Ionization for Generic Ions (V. Ivanchenko)
• New model of Transition radiation (V. Grichine)
• for TR detectors
• Redesign of few processes
• prototype model approach for Ionization and
  Bremsstrahlung (V. Ivanchenko)

9
Multiple scattering
15.7 MeV electrons on gold foil

• Small differences between G4 G3 observed below
  1 MeV
• Results competitive versus data in G4 3.2
• Differences traced to Multiple Scattering
• MS modeling improved in Geant4 4.0 5.0
• Examples of comparisons to data
• Thanks to L. Urban

Geant4 4.0 (Dec 2001)
Angle (deg)
10
Multiple scattering

• Refined modeling of angular distributions
• in Geant4 5.0
• Modeling comparisons
• L. Urban

Geant4 5.0 (Dec 2002)
Angle (deg)
11
Hadronic physics models, processes and lists
Components can be assembled in an optimized way
for each use case.

• Five level implementation framework
• Variety of models and cross-sections
• for each energy regime, particle type, material
• alternatives with different strengths and CPU
  requirements.

Pre-compound model

• Illustrative example of assembling models into an
  inelastic process for set of particles
• Uses levels 1 2 of framework

Parame- terized
12
Models Cascade energy range

• Parameterized process (1997)
• Chiral Invariant Phase Space decay,CHIPS
• For g-Nucleus, p capture, string-backend
• First release Dec 2001 in Geant4 4.0
• Refinements and extension in 2002
• Bertini cascade (Dec 2002, Geant4 5.0)
• Re-engineered from HETC by HIP
• See the presentation of A Heikinen
• Binary cascade model (Frankfurt, CERN)
• First release for nucleon induced interactions
  (in G4 5.0)
• Extensive verification suite
• See the presentation by D. Wright, V. Ivantchenko
  
• For further details,
• see the next presentation (J.P. Wellisch)

M Kosov, P Degtyarenko, JP Wellisch
A Heikinen N Stepanov JPW
G Folger JPW
13
Tailored Physics lists

• Created and distribute educated guess physics
  lists
• That correspond to the major use cases of Geant4
  involving hadronic physics,
• to use directly, and as a starting point for
  users to modify,
• facilitate the specialization of those parts of
  hadronic physics lists that vary between use
  cases.
• First released in September 2002
• Using physics models of Geant4 4.1.
• Revised with experience of comparisons with data
• Latest
• updated with physics models of Geant4 5.0 in
  March 2003
• Find them on the G4 hadronic physics web pages
  http//cmsdoc.cern.ch/hpw/GHAD/HomePage

14
Use cases of Physics Lists

• HEP calorimetry.
• HEP trackers.
• 'Average' HEP collider detector
• Low energy dosimetric applicationswith neutrons
• low energy nucleon penetration shielding
• linear collider neutron fluxes
• high energy penetration shielding
• medical and other life-saving neutron applications

• low energy dosimetric applications
• high energy production targets
• e.g. 400GeV protons on C or Be
• medium energy production targets
• e.g. 15-50 GeV p on light targets
• LHC neutron fluxes
• Air shower applications
• low background experiments

Contributors http//cern.ch/geant4/organisation/
working_groups.htmlwg.Had
15
Physics lists for calorimetry

• LHEP is the fastest for CPU
• uses the LEP and HEP parameterized models for
  inelastic scattering.
• QGSP,
• uses theory-driven modeling for reactions of ps,
  Ks, and nucleons.
• It employs
• Quark Gluon String Model
• for the 'punch-through' interactions of the
  projectile
• A Pre-equilibrium decay model
• with an extensive evaporation phase to model
  the nucleus 'after the punch'.

• QGSC, is similar but uses CHIPS for fragmentation
• The CHiral Invariant Phase-Space decay (CHIPS)
• FTFP replaces instead the string
• with a diffractive string excitation
• similar to that in FRITJOF, and the Lund
  fragmentation functions.

16
Comparison projects

• Joint efforts for comparing Geant4 with
  experiment test-beam data.
• Results of EM comparisons peak between
  2000-2002.
• Hadronic comparisons 2002-ongoing.
• Collaboration with experiments
• ATLAS (projects with data of numerous test beams)
• BaBar (with data for tracker, drift chamber)
• Many results have been presented at conferences
  workshops, eg Calor 2002.
• And at regular LHC experiment-Geant4 physics
  comparisons meetings

17
Resolution

• Original (org) results from Calor 2002
  presentation,
• (March 2002).
• Open symbols from additional physics lists JPW,
  May 2002, using geant4 4.0-patch2
• (released end Feb 2002).

Status of May 2002 Updated results in subsequent
talks
Thanks to Atlas HEC and J.P. Wellisch
18
Linearity

• Mix and match problem seen in parameterised
  models.
• Problem disappears, as expected, when utilising
  theoretical models
• Eg Quark-Gluon String Model CHIPS
• For latest results please see the presentations
  of JP Wellisch Atlas

First results from April/May 2002
Thanks to Atlas HEC and J.P. Wellisch
19
As presented at Geant4 Workshop, 30th September
2002
Thanks to P. Loch, Atlas
Geant4 Hadronic Signals in ATLAS Calorimeters

• Calorimeter pion response
• after discovery of mix-and-match problem
  (transition from low energy to high energy
  char-ged pion models) in the deposited energy
  from energy loss of charged particles in pion
  showers in the HEC (G4 4.0, early 2002) fixes
  suggested by H.P. Wellisch (LHEP, new energy
  thresholds in model transition code changes)
  and QGS model tested
• e/p signal ration in HEC and TileCal still not
  well reproduced by Geant4 QGS or LHEP - but
  better than with GCalor in Geant3.21
• energy dependence in HEC in QGS smoother,
  discontinuities between 20 GeV and 80 GeV
  gone

e/p signal ratio
HEC Pions
QGS
LHEP
e/p signal ratio
Pion energy GeV
Word highlights JA, March 2003
20
New capabilities
Part 3

• Detector description
• Performance
• Visualisation

21
Other Development highlights

• Detector description
• New ways to create geometries
• Tools to detect incorrect geometry definitions
• A different field for any volume (or volume tree)
• Overriding a global field
• Ability to reduce initialisation time
• By saving/retrieving physics processes table
• Variance reduction / event biasing
• Importance biasing by geometry
• Leading particle biasing

22
Improvements in Geometry

• Reflection of volume hierarchies
• Eg to create endcap geometry
• Improved voxelisation for performant navigation
• 3-D for parameterized volumes
• Now equal performance to placed volume
• Option to avoid voxelizing some volumes
• Illegal geometries detected rejected
• E.g. incompatible daughters (placed
  parameterized)
• XML binding GDML 1.0 released
• Specification Implementation
• Refinements currently on hold.

I Hrivnacova G Cosmo V Grichine
G Cosmo
G Cosmo
R Chytracek
23
Debugging geometries

• It is easy to create overlapping volumes
• a volume that protrudes from its mother,
• 2 volumes that intersect in common mother
• During tracking Geant4 does not check for
  malformed geometries
• The problem of detecting significant overlaps
  is now addressed by
• DAVID that intersects volumes directly
• ( Uses graphical representations )
• Created by S. Tanaka, released ca 1997
• New commands to run verification tests
• Created by DC Williams released in 4.0
• New example with full tracking / navigation
• Created by M Liendl released in 5.0

Thanks to S. Tanaka
24
Variance reduction

• Geant4 had leading particle biasing option for
  low energy neutrons.
• Now redesigned and improved, implementation in
  Geant4 4.1.
• It was possible to use other methods, but only in
  user code.
• Now new general purpose built-in methods have
  been released
• Further refinements methods are under
  development.
• Importance biasing
• Splitting/Russian roulette (first released in G4
  4.1, June 2002).
• Importance values can be associated to a volume
• In the mass geometry or in a dedicated
  parallel geometry.
• Enabling simulation of shielding applications
  with improved time efficiency by large factors
• Varied options in driving MC history and
  scoring tallies
• No changes to the kernel were required, due to
  the flexibility of the toolkit.
• Leading particle biasing
• a-la MARS 95, for Enlt5GeV

M Dressel
N.Kanaya
25
CPU Performance

• Our first simple benchmarks
• Geometry faster, EM shower setups competitive
• Performance in experimental setups (with Geant4
  releases 2 and 3) was comparable to Geant3
• few counterexamples, including BTeV ECAL.
• New performance issues arose with Geant4 4.0
• and were addressed (in the patches release 4.1)
• Difficult cases remain, including
• Some setups of EM showers and field propagation,
  factor 2x
• Collecting a set of benchmarks
• To follow computing performance regularly
• Goal is that Geant4 is at least as fast as Geant3
  in almost all cases
• When its power is used.

26
Visualization
DAWN renderer Thanks to S. Tanaka

• Geometry, hits
• New
• DTREE hierarchy display
• HEPREP driver for WIRED
• Other Current Drivers
• OpenGL
• VRML
• DAWN Renderer
• Also from others, eg
• IGUANA (for CMS simulation)

Iguana, thanks to L.Tuura, I. Osborne
27
Current development highlights
Part 4

• Imminent
• Scheduled

28
In Progress 2003 (highlights)

• Cuts per region
• See next slides
• Improvements of multiple scattering
• in straggling, backscattering
• Additional refinements of physics lists
• Continuous updates
• Design iteration of EM (std) processes
• With benefits in tailoring, maintenance
• Further extension and automation of testing
• Statistical testing benchmarks and test-beams

29
Cuts in Geant4 (to date)

• Geant4 has had a unique production threshold
  (cut) expressed in length (range of secondary).
• For all volumes
• Possibly different for each particle.
• This promotes
• Clear criteria for locality of energy deposition
• better use of CPU less wasted in dense
  materials
• Yet appropriate length scales can vary greatly
  between different areas of a large detector
• Eg a vertex detector (5 mm) and a muon detector
  (2.5 cm).
• Having a unique (low) cut can create a
  performance penalty.
• So the part of the detector with the lowest cut
  need fixed the cut for all the simulation.

30
Motivation for several cuts

• Having a unique cut enforced a choice between
• Sacrificing accuracy of energy deposition
• Accepting a performance penalty
• Lifting the uniqueness of cuts
• Requested from LHC experiments BaBar
• Implemented by introducing geometrical regions
• And enabling the choice of thresholds in a region.

31
Region its properties

• Introduce the concept of  region 
• Set of geometry volumes, typically of a
  sub-system
• Eg barrel end-caps of the calorimeter
• Or any group of volumes
• A cut in range is associated to a region
• a different range cut for each particle is
  allowed in a region .
• Typical Uses
• barrel end-caps of the calorimeter can be a
  region
• Deep areas of support structures can be a
  region.

Region B
Region B
Region B
Region C
c
Region B
Region A
32
Cuts per region status

• Design and implementation have been made
• without severe design revision of the existing
  GEANT4
• First implementation available in latest b
  release (Feb)
• Comparable run-time performance
• Today a penalty within 5 is seen, due to
  redundant checks included for verification
  purposes
• Full release will be in Geant4 5.1 (end April)
• With further refinements, tests, validation.

33
MS in progress

• Multiple scattering
• Refinements
• Backscattering
• Straggling
• Transmitted energy

34
Multiple scattering latest
Electrons of 1MeV incident on Al
35
MS straggling
Fit to data
Lateral straggling of 2.5 MeV protons After mylar
foils
Geant4 5.1 (April 2003)
36
In progress (also)

• The refinement of the design of EM physics
  processes through the use of models.
• To enable the specialization of key features
• To enable the easy use of different models for a
  single process (e.g. Ionization) in one
  application.
• Additional variance reduction techniques
• Filter for enhancing processes in hadronic
  interactions.

37
Some further 2003 development highlights

• Additions to physics processes/models
• p induced binary cascade model, ..
• EM-std implementation with model approach.
• Refinements, including
• Improvement to recoil in elastic scattering
• Improved X-sections for pions.
• Revisions of the tailored physics lists
• Incorporating results of validation
• Variance reduction
• Physics process enhancement
• Leading particle biasing
• Plus refinements to importance biasing

38
Review and Releases

• d Review October 2002
• Report available at http//cern.ch/geant4
• Developments available in b releases
• Every two months
• Latest b release (February)
• Included cuts per region
• Upcoming releases
• Next minor release is Geant4 5.1 planned for
  end-April
• Incorporating cut per region, developments in
  progress.
• Release timeframe selected to aid in CMS
  production.
• Scheduled release Geant4 5.2 for end-June
• Further refinements, developments
• 2003 work items planned release contents to be
  available soon
• Started from User Experiment Requirements and
  Requests
• Next major release Geant4 6.0 is scheduled for
  December 2003.

39
Summary
http//cern.ch/geant4/

• Results of comparing Geant4 versus data,
• Have are providing excellent yardsticks of EM
  perf.
• Are testing the hadronics well, with increasing
  coverage
• Geant4 has demonstrated important strengths
• stability of results, flexibility, transparency.
• it is in production use today in running HEP
  experiments (BaBar, HARP)
• Geant4 is evolving
• With the feedback from LHC exper., BaBar and
  numerous other experiments and application
  domains.
• Refinements development are ongoing.

40
THE END

• Thanks to all
• Contributors
• Users

41
After the END

• Slides after this are backups,
• not part of the presentation.

v0.8 24th March 2003, 1840 GMT
42
Electromagnetic physics

• Gammas
• Gamma-conversion, Compton scattering,
  Photo-electric effect
• Leptons(e, m), charged hadrons, ions
• Energy loss (Ionisation, Bremstrahlung) or PAI
  model energy loss, Multiple scattering,
  Transition radiation, Synchrotron radiation,
• Photons
• Cerenkov, Rayleigh, Reflection, Refraction,
  Absorption, Scintillation
• High energy m
• Alternative implementation
• Standard for applications that do not need to
  go below 1 KeV
• Low Energy down to 250eV (e/g), O(0.1) mm for
  hadrons
• Including specialized HEP applications

43
Shower profile

• 1 GeV electron
• in H2O
• G4,
• Data
• G3

44
Liquid Argon Hadronic Calorimetry

• Electrons
• Geant4 predicts less visible energy in LAr than
  Geant3 (3) and more energy in absorber (0.1).
  Total energy is the same
• energy resolution well reproduced by Geant3
  Geant4 gives too good resolution
• Pions
• first results of simulation with Geant4 look
  reasonable
• more detailed comparisons with test beam data in
  progress
• open questions being discussed with Geant4 people

pion energy resolution inLAr Hadronic End Cap
March 2002, Atlas HEC
45
Support new continued

• Documentation
• Revisions of the user and reference guides
• After assessments of overall structure detailed
  
• LXR for code reference
• see http//geant4www.triumf.ca/lxr/
• New tool for collecting requirements
• Continued Support
• of users questions, problems
• HyperNews, Problem reporting system, email.
• of comparisons with data
• By wide variety of users, in HEP, space, medical
  phys., ..

46
Testing and QA 2002/3

• Establishment of statistical testing suite
• Automated comparison of physics quantities
• Against standard data (eg NIST)
• In test-beam applications
• Including regression testing.
• For details see
• Establishing a benchmark suite for computing
  performance.

47
Examples of improvements

• Fixes and improvements in Geant4 release 4.1
  (June 2002)
• Geometry
• Fix for voxelisation of reflected volumes
• Fix for exit normal angle
• Fix for problem in very small step in field
• EM
• Improvements in Multiple Scattering, Ionisation,
  ..
• Hadronics
• Fix for energy conservation in parametrised
  models.
• Fix for small peak at f0 in parametrised models.

48
BaBar

• Geant4 based simulation since 2001 production.
• More than 109 events (through Oct 2002)
• Used Geant4 3.1fixes, own transport.

49
GEANT4

• 5cm Pb, CO2, Pb, CO2

Cut 2mm Pb 2.5 MeV CO2 55keV
GEANT3
50
New Viz functionality

• New commands, with better control
• DTREE
• Output of geometry tree
• To ascii
• Visualisation of Boolean solids
• Future
• DCUT slice view in multiple drivers
• Improved DrawTrajectory()
• Curved trajectory handling

51
Cuts/Region Introduction

• A Cut here is a  production threshold 
• Only for physics processes that have infra-red
  divergence
• Not tracking cut (which does not exist in
  Geant4)
• GEANT4 up to now allows a unique cut in range
• One cut in range for each particle
• By default is the same cut for all particles
• Consistency of the physics simulated
• A volume with dense material will not dominate
  the simulation time at the expense of sensitive
  volumes with light material.
• Requests from ATLAS, BABAR, CMS, LHCb, , to
  allow several cuts
• Globally or per particle

52
Geant4 Collaboration
Collaborators also from non-member institutions,
including Budker Inst. of Physics IHEP
Protvino MEPHI Moscow
Lebedev